Generally, a coaxial cable is a transmission line comprising an inner conductor for signal transmission and a shield layer formed on a concentric axis of the inner conductor, when the coaxial cable is viewed in cross section, the inner conductor and the shield layer form concentric circles, and an insulating layer having a dieletric property is formed between the inner conductor and the shield layer.
The coaxial cable has been developed as various products according to size and kind, and due to structural characteristics, the coaxial cable has a small change in attenuation or transmission delay of a signal according to frequency and can transmit simultaneously a large capacity data. And, even when a plurality of coaxial cables are received in a single cable, signal leakage between the coaxial cables is insignificant.
FIG. 1 is a view illustrating a structure of a conventional coaxial cable, and as shown in FIG. 1, the conventional coaxial cable comprises an inner conductor 11, an outer conductor (metal shield layer) 17, a polymer insulating layer (dielectric layer) 13 formed between the inner conductor 11 and the outer conductor 17, and a protective coating layer 19 formed along the outer periphery of the outer conductor 17.
The development trend of the conventional coaxial cable moved toward improvement of a structure between the inner conductor and the outer conductor for reducing the loss of transmission energy or improvement of dielectric characteristics for enhancing the transmission speed. In particular, with the recent development of an advanced information-oriented society, there is an increasing demand for high speed transmission of a device for testing/inspecting an information communication equipment and a semiconductor device used in such an equipment.
Meanwhile, as a mobile phone or a ultrathin equipment of high definition gets smaller in size, a micro coaxial cable having a diameter of 1 □ or less is developed lively to drive the small-sized equipment. Like the conventional coaxial cable, the micro coaxial cable comprises basically an inner conductor, an insulating layer, an outer conductor and a protective coating layer. However, the micro coaxial cable is received in a small-sized equipment, and thus should provide a long-term uniform reliability in a severe environment such as rotation or bending. Recently, a mobile phone or a ultrathin equipment of high definition is manufactured in the form of bending and/or rotation, and accordingly, the micro coaxial cable received in such an equipment should provide a long-term uniform reliability in a severe environment such as bending or rotation.
However, as mentioned above, the conventional coaxial cable has been developed to enhance transmission speed or reduce the loss of transmission energy, but did not show any development progress for providing a long-term uniform reliability in a severe environment such as bending or rotation.